It is known that certain compounds, like substituted benzoic acid herbicides and phenoxy-substituted carboxylic acid herbicides, possess selective herbicidal activity against broadleaf vegetation at dosages as low as a few ounces of active herbicide per acre. The substituted benzoic acid and the phenoxy-substituted carboxylic acid herbicides have been applied to susceptible vegetation in their acid form, but herbicidal effectiveness was poor because the water-insoluble acid form these herbicides did not sufficiently penetrate the leaves of susceptible vegetation for fast and efficient eradication.
Therefore, the substituted benzoic acid herbicides and the phenoxy-substituted carboxylic acid herbicides, and other herbicidal compounds including a carboxylic acid functionality, traditionally were converted from the acid form to an ester form or to a salt form to enhance water solubility and leaf penetration properties. Both the ester forms and the salt forms of these herbicidal compounds are available commercially and are provided as liquid products including a known, but variable, amount of the active herbicide. A predetermined amount of water then is added to dilute the active herbicide before spraying the susceptible vegetation. The predetermined amount of water is related to the concentration of the active herbicide in the liquid herbicidal product and the desired strength of the spraying solution.
In general, the ester forms of these herbicides are provided as petroleum distillate-based emulsifiable concentrates that are diluted with water. The resulting herbicide emulsion then is sprayed on the vegetation to be controlled. The salt forms of these herbicides are provided as concentrated aqueous solutions that are diluted with water. Then the resulting aqueous herbicidal solution is sprayed on the vegetation to be controlled. For reasons of economy and safety to the environment and the herbicide applicator, the aqueous-based salt form of the herbicide often is the preferred form of the herbicide. As will be discussed more fully hereinafter, some solid forms of these herbicidal compounds also are available.
In particular, the ammonium salt, various alkylamine and alkanolamine salts, and the alkali metal salts of the substituted benzoic acid herbicides and the phenoxy-substituted carboxylic acid herbicides, and other herbicidal compounds including a carboxylic acid functionality, have been used as selective herbicides for controlling a wide range of broadleaf weed species, particularly in cereal crops, in gardens and in turf maintenance. These herbicidal compounds have been provided in a salt form as concentrated aqueous solutions, in an ester form as concentrated solutions of a petroleum distillate-based solvent or in the form of solid granules including an inert, and usually water insoluble, support material incorporating an acid, ester or salt form of the herbicidal compound. Both the liquid and granular herbicidal compositions can include a single herbicide or a mixture of herbicides, depending upon the herbicide combination best suited to control a particular weed species.
The concentrated, aqueous herbicidal salt solutions are supplied to the consumer, or applicator, in plastic or metal containers. The applicator charges a measured amount of the herbicidal salt solution into a mixing vessel or tank, then the concentrated herbicidal salt solution is diluted to the desired concentration by adding sufficient water to the mixing vessel or tank. The diluted herbicidal salt solution then is sprayed onto the crop, or onto the turf, at the appropriate dosage rate.
The amount of active herbicidal salt present in the concentrated aqueous herbicidal salt solution is limited by the water solubility of the specific salt of a particular herbicide. The amount of active herbicide, as a salt, in the aqueous solution therefore is limited to a maximum of about 85% by weight of the solution. However, several salts of several different substituted benzoic acid herbicides and phenoxy-substituted carboxylic acid herbicides have demonstrated a much lower solubility in water.
Therefore, the formulation of substituted benzoic acid herbicides or phenoxy-substituted carboxylic acid herbicides, and of other herbicidal compounds including a carboxylic acid functionality, into aqueous, or petroleum distillate-based, liquid concentrates has demonstrated several disadvantages. The petroleum distillate-based liquid concentrates have the disadvantage of being expensive and combustible, and of possessing sufficient volatility to harm beneficial nearby vegetation, in addition to presenting additional health and environmental concerns beyond those posed by the herbicidal compound itself. Furthermore, both the petroleum distillate-based and the aqueous concentrates include a significant amount of solvent that adds to the size, weight and cost of containers, transportation and handling In addition, the disposal of empty herbicide containers results in potential hazards to the environment because of possible ground contamination by any residual herbicide remaining in the container, and by the non-biodegradability of the herbicide container itself.
Many of these disadvantages are not overcome by using a granular form of the herbicidal compound, wherein the herbicidal compound is impregnated into or absorbed onto an inert support. In the granular form, the herbicide product is supplied in a plastic bag, a plastic drum or a fiber keg. The granular herbicide product is applied to vegetation by directly spreading the herbicide granules onto the vegetation at a suitable dosage rate. The granular herbicide products generally have an active herbicide content in the range of from about 0.5% to about 50% by weight. Similar to the liquid herbicidal concentrates, the volume and weight of the inert support material increase the size and cost of the container, and the costs of transportation and handling, of the granular herbicide product. In addition, the disposal of empty herbicide containers poses the same adverse environmental concerns as discussed above in regard to the concentrated liquid herbicide products.
Therefore, it would be advantageous to provide a highly-concentrated herbicidal composition, in the form of a solid, and preferably a powder, that can be added to water at the application site, and that dissolves quickly and essentially completely, in hard or soft water, to provide an aqueous solution of the herbicidal compound that can be applied directly to the crop or to the turf, or that can be diluted further as necessary. Such a highly-concentrated, solid herbicidal composition reduces container, shipping and handling costs. More importantly, and as will be discussed more fully hereinafter, if the highly-concentrated, solid herbicidal composition is sufficiently dry, such as including less than 3%, and preferably less than 1%, water, the herbicidal composition then can be supplied in water-soluble packets. Water-soluble packets including a water-soluble herbicidal composition would eliminate direct contact between the applicator and the herbicidal composition, such as occurs during dilution of a concentrated liquid herbicidal composition, and would eliminate the need to dispose of an empty herbicide container. Accordingly, safety to the applicator and safety to the environment are enhanced.
As previously stated, water-soluble forms of substituted benzoic acid herbicides, phenoxy-substituted carboxylic acid herbicides, other herbicidal compounds including a carboxylic acid functionality and bentazon are known. Specifically, the lithium, sodium and potassium salts of 2,4-dichlorophenoxyacetic acid (2,4-D) and related phenoxy herbicides have ben reported in the literature and in patents, and have been marketed. For example, Morrill U.S. Pat. No. 2,519,780 discloses aqueous solutions of alkali metal, ammonium and alkylammonium salts of 2,4-D that further include an ethoxylated fatty acid to help prevent the precipitation of the 2,4-D salt in hard water. Other patents disclosing aqueous solutions of substituted benzoic acid or phenoxy-substituted carboxylic acid herbicides include: U.S. Patent Nos. 2,522,488; 2,606,876; 2,694,625; 2,992,913; 3,081,162; 3,103,432; 3,248,208; 3,284,186; and 4,123,253. Granular herbicidal compositions including an herbicide impregnated into or absorbed onto an inert support are disclosed for example in Kenney, Jr. et al. U.S. Pat. No. 2,695,839; Wright U.S. Patent No. 2,792,295; Galloway U.S. Patent Nos. 3,056,723 and 3,168,437; Ordas U.S. Patent No. 3,421,882; Hokama U.S. Pat. Nos. 3,870,732, 3,910,974, 4,022,610; and Poignant et al. U.S. Pat. No. 4,013,451.
As previously indicated, the substituted benzoic acid herbicides and the phenoxy-substituted carboxylic acid herbicides generally are manufactured, and marketed, as liquid concentrates or as granules including an inert support. However, some dry salts of these and other herbicidal compounds also have been disclosed and marketed. For example, Richter, in U.S. Pat. No. 3,012,870, discloses the preparation of the sodium, ammonium, dimethylammonium and other salts of 2-methoxy-3,5-dichlorobenzoic acid in an organic solvent. The salts disclosed by Richter then were admixed with an inert support and applied as a dust. Guth, in U.S. Pat. No. 3,023,096, discloses the manufacture of potassium and lithium 2,4-dichlorophenoxyacetate. The lithium salt of 2,4-D is available commercially, under the commercial tradename, LITHATE, from Guth Corporation, Naperville, Ill., as a 95% active lithium 2,4-D composition. Other patents disclosing the preparation, or use, of solid phenoxy or benzoic acid herbicidal salts include Guth, U.S. Pat. Nos. 3,103,432 and 3,208,843; and Kauffman, U.S. Pat. No. 3,940,260.
The lithium salt of 2,4-D is a stable, dry compound and is highly water-soluble. However, the lithium salt of 2,4-D also possesses several disadvantages. For example, lithium is expensive, and lithium can accumulate to toxic levels in the soil. Furthermore, the lithium salt of 2,4-D is a slow acting herbicidal salt compared to other salts of 2,4-D, like the dimethylamine salt. Therefore, it would be advantageous to provide a dry, highly-concentrated salt of an herbicidal compound that includes a carboxylic acid functionality, like a phenoxy-substituted carboxylic acid herbicide salt or a substituted benzoic acid herbicide salt, that does not possess the disadvantages of the lithium salt. It is known that the ammonium, the alkylamine and the alkanolamine salts of 2,4-D and related phenoxy herbicides overcome the disadvantages presented by the lithium salt, but such salts have been difficult to prepare as dry herbicidal salt compositions including at least 90% by weight of the active herbicidal salt. As will be demonstrated more fully hereinafter, the method of the present invention provides such dry and highly-active herbicidal salt compositions.
A solid form of the dimethylamine salt of 2,4-D also is available commercially from Platte Chemical Co., Fremont, NB., under the brand name SAVAGE. This product includes 95% by weight of the dimethylamine salt of 2,4-D and is water soluble. This product has a pH of approximately 9 and has a "fishy" amine-like odor, thereby indicating that SAVAGE includes an excess amount of dimethylamine to ensure complete water solubility of the product. The presence of excess amine however provides a solid herbicidal composition, and solutions derived therefrom, that have an offensive odor and that are generally unpleasant to use. As will be demonstrated more fully hereinafter, the method of the present invention provides an herbicidal salt composition that does no include excess amine, and can be deficient in amine, and that is still completely water soluble. The elimination of excess amine, while maintaining complete water solubility, is surprising and new in the art. The elimination of excess amine also avoids the unpleasant odor from the composition and provides herbicidal solutions having an essentially neutral pH of about 5 to about 7, thereby overcoming the potentially corrosive properties of an herbicidal solution having a high alkaline pH.